An image forming apparatus such as a printer, a copying machine, a facsimile or the like has a sheet feeder for separating sheets (recording media) to feed them to an image recording unit thereof sheet by sheet.
Publication of Japanese Unexamined Patent Application No. 2005-247550 (refer to FIGS. 3 to 9. Hereinafter, Patent Document 1) disclosed a sheet feeder that includes a sheet feeding cassette in which a plurality of sheets are stacked and a feed roller provided at a lower end of a feed arm that is disposed above the sheet feeding cassette in such a manner as to oscillate vertically. In addition, a sloping separation plate is provided at a down stream end portion of the sheet feeding cassette in a sheet feeding direction, and a sheet separation member is provided in a central portion of the sloping separation plate in a lateral direction thereof (a sheet width direction). This sheet separation member is such that claw-like projecting portions, arm portions which support the projecting portions from both sides thereof and leaf spring portions are formed on a base portion made of a metal sheet at predetermined intervals through press work, and the leaf spring portions are formed integrally with the base portion to support the sheet separation member on a rear surface of the sloping separation plate. The claw-like projecting portions are set to project a predetermined amount from elongated openings which are opened in a central portion of the sloping sheet separation plate along the sheet feeding direction. Thus, the feed roller, that is rotating, feeds a topmost sheet while pressing against an upper surface of the topmost sheet. As this occurs, leading edges of the sheets so stacked are brought into engagement with the projecting portions, whereby the stacked sheets are loosened so that only the topmost sheet is separated to be fed.
Publication of Japanese Unexamined Patent Application No. 2004-067389 (refer to FIGS. 4 to 6. Hereinafter, Patent Document 2) disclosed a sheet feeder that includes a sheet feeding cassette main body that is opened in an upper surface thereof to accommodate sheets in a substantially horizontal state. A sloping surface is provided at a downstream end of the sheet feeding cassette main body in a sheet feeding direction, and a sheet separation guide is provided on the sloping surface. A plurality of projections are formed on the surface of the sheet separation guide. The projections are highest at a lowest portion of the sheet separation guide, and the projections decrease gradually their height at predetermined intervals towards an upper end of the sheet separation guide. In this way, the friction coefficient of the projections with the end portions of the sheets is set to gradually decrease from the lower projections towards the upper ones. In addition, the projections are formed in a plurality of rows in a sheet width direction.